THOR Global Defense Group TR-15 carbine, manufactured along the lines of US GI M4, but fitted with a number of accessories such as AAC silencer, Vltor rail forend and buttstock, and Trijicon ACOG 4X optical sightimage: THOR Global Defense Group

The Colt company developed various carbine versions of the basic AR-15 / M16 rifle since 1970s. These carbines were intended for all markets - military, law enforcement, civilian. US Military (and some other armies, most notably - Israeli Self-Defense Forces) had adopted the Colt CAR-15 Commando and XM-177 carbines during the 1970s and 1980s. But early in 1990s the old idea of replacing the pistols in the hands of the troops with some more effective, shoulder fired weapon, rise again in the heads of the US Military. In fact, this idea can be dated back to the US M1 Carbine of 1941, but good ideas never die. So, in the 1994, US Army adopted the Colt Model 720 selective-fire carbine (basically, a shortened M16A2 rifle), as the US M4 Carbine. This weapon was intended to replace in service some M9 pistols, as well as some aged M3A1 submachine guns and some M16A2 rifles. New weapon was much more handy and comfortable to carry, than the long M16A2 rifle, so the US Special Operations Command (SOCOM) put its eye on the M4 as a possible universal weapon for all Special Operations community. For this purpose M4 was latter modified with the M16A3-style flat-top receiver with integral Picatinny-type accessory rail instead of the M16A2/M4-type integral carrying handle. This modificatin retained the M4 index. The only difference between the M4A1 and M4 is that its trigger unit of M4A1 is modified to fire full-auto instead of the three shots bursts in M4. Specially for the SOCOM M4A1s US Naval Surface Warfare Center developed a SOPMOD M4 kit, that consisted of the M4A1 carbine equipped with Rail Interface System (RIS) instead of the standard handguards. The kit also includes a variety of the add-on goodies, such as various sights (ACOG 4X telescopic, ACOG Reflex red-dot, detachable back-up open sights), laser pointers (visible and infra-red), detachable sound suppressor (silencer), modified M203 40mm grenade launcher (with shortened barrel and improved sights). The kit also included a detachable front grip and tactical light.

At the present time, the M4 carbine is used as a front-line weapon by US Army, Marine Corps and SOCOM operators in Iraq and Afghanistan. Combat experience with thos weapon resulted in update program, which will, as of now (mid-2010) following steps. First, Army wanted to install heavier barrel to allow more sustained firepower, combined with full-automatic mode of fire instead of 3-round burst, and ambidextrous safety/selector switch. Second stage will see improved rail adapter and a new, improved bolt carrier, and a possible third stage will include change of operating system (most probably, from direct gas to the gas piston).

At the present time, the Colt company still is the the prime M4 carbine manufacturer for US Armed forces, but many other companies build similar "milspec" weapons for other US and foreign customers, such as government and private security organizations, law enforcement etc. To name just few, M4-type carbines are manufactured by Bushmaster Firearms, Olympic Arms, THOR Global Defense Group and others

Technical description.
The M4 carbine differs from the M16A2 rifle only by having a shorter barrel and a telescoped, 4-position buttstock. The M4A1 is a similar modification of the M16A3 rifle, so for general technical description please refer to the M16 article on this site.

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